Theresa May is preparing to visit Africa for the first time since becoming prime minister in 2016.
May will fly to South Africa on Tuesday before travelling to Nigeria and Kenya as part of a trade mission aimed at boosting post-Brexit fortunes.
The prime minister said the trip would be a "unique opportunity at a unique time for the UK".
She added the UK wanted to "deepen and strengthen its global partnerships" as it prepared to leave the EU in 2019.
May will be accompanied to the three countries - all of them Commonwealth countries - by a 29-strong business delegation, says a BBC report.
Security issues will also feature on her agenda and she is expected to discuss the threat of Boko Haram in Nigeria, and the role of British troops based in Kenya who are helping countries fight al-Shabab militants in Somalia.
May's visit to Nairobi will mark the first by a UK prime minister to Kenya since Margaret Thatcher in 1988.
It is also the first to Sub-Saharan Africa by a British leader since David Cameron in 2013 for Mandela's memorial service.
May said a "prosperous, growing and trading Africa" was "in all of our interests", adding the continent's "incredible potential will only be realised through a concerted partnership between governments, global institutions and business".
A Downing Street spokeswoman added: "The PM will use the visit to announce further support to tackle instability across the region, because nations can't prosper without it."
During her time in South Africa, May is also due to present a World War One relic - linked to one of the worst maritime disasters in English waters - to Ramaphosa.
The SS Mendi sank off the Isle of Wight in 1917 killing more than 600 black South Africans en route to the Western Front to support British troops.
The ship's bell was given to BBC reporter Steve Humphrey in 2017 in a plastic bag at Swanage Pier, Dorset, after an anonymous phone call - and will now be handed back by May.